1. Field of Invention
This invention pertains to the art of filtration wherein disposable filter cartridges are employed to clarify a variety of liquids or gases where the inward flow of particle laden fluid customarily penetrates the outer surface of the cartridge and then emerges from the inner surface to be carried away along the interior of a tubular core. The invention relates to an improved filter cartridge that is dimensionally and structurally stable, simple to construct, and which gives unexpectedly good performance in terms of filtration efficiency and useful life.
Filter cartridges can be conveniently classified into two fundamental types, (a) the pleated sheet or surface filtration type, and (b) the bulk or in depth filtration type. The present invention belongs in the second category.
One type of filter cartridge that is widely known and has received wide reception and usage is that described in detail by Goldman, in U.S. Pat. No. 1,958,268, the cartridge being formed by winding a continuous strand or roving of fibrous material around a central perforated core in criss-cross fashion in a sufficient number of layers to create a filter cartridge of the desired diameter. The resulting structure is provided with a multiplicity of helically disposed, diamond-shaped openings extending radially inward from the outer peripheral surface of the filter media to the core. As the strand or roving of fibrous material is being wound onto the core, it is subjected to a napping operation to pull a certain amount of the fibers away from the strand or roving so as to create a network of fine fibrous material across the diamond-shaped openings. It is essentially this napped fibrous material pulled from the strands or roving that performs the filtering function, and the superimposed layers of stranded material are relied upon to hold the napped material in place so that it will function effectively. This technique of napping and securing of the napped material is difficult to control to the extent necessary to be totally reliable and to provide uniform filtering capability throughout the filter material, as well as resulting in an obvious weakening of the strands or roving.
More recently a variation of the same type of filter cartridge has been described by Goldman in U.S. Pat. No. 3,065,856, in which an apparent effort was made to avoid the deficiencies and draw backs of the napping technique. In this patent, Goldman has described a filter cartridge made by laying down a stranded material or roving, while simultaneously depositing a thin fibrous membrane between each layer of the roving from the core to the outer periphery to provide a filtering septum in place of the napped portion of the fibers. However, the provision of this added component throughout the structure of the filter material results in further undesirable expense and complexity of fabrication. Another cartridge filter design has been described by Fogwell in U.S. Pat. No. 2,742,160, in which a mat of filter material is wound around a core. While being wound, the mat is carried on a supporting fabric-like material which covers one face and both sides of the mat. As in the Goldman patent, the provision of support material adds to the expense and complicates the fabrication of the resulting filter cartridge.
Other less expensive types of fibrous or granular filter cartridges have been found unsatisfactory for many filtering purposes for one or more reasons, such as lack of uniformity and consequent unreliability, shortness of life expectancy, or failure to provide the permanent integrity and strength of structure and lasting dimensional and structural stability to be found in the above-described stranded or roving design.
It is an object of the present invention to provide for the first time a fibrous filter cartridge and a process for making the same, wherein such cartridge is facile and economical to fabricate, and at the same time will provide in its structure the desirable reliability of uniformity of filtering performance while retaining a dimensional stability and integrity heretofore found only in more complicated filters.
It is also an object of this invention to provide a simple fibrous filter element or cartridge and process for making the same, wherein such cartridge combines a high filtering capacity with respect to both the volume of fluid and effective filtering life.
It is a still further object of this invention to provide a filter cartridge and process for making the same, wherein such cartridge is especially adapted for the effective filtration of paints and similar products for extraction of particles of a selected range of particle size.
These and other objects and advantages of the present invention will become apparent from the following detailed description.